Play 1 hour games and always use a real chess board. Good for concentration.
A normal game between good players last about 40 moves. That it 1,5 minutes per move in an 1 hour game. When you have some opening repertoire you play a little faster the first 5+ moves and get a small reserve there. Use your time, look at a clock and think/move in an even pace. Ask yourself a few questions before every move: is there a threat? have I done my development? can I improve a piece or pawn placement? That is enough for a long time and you win with no mistakes.
Fast chess is always worse chess.
Have patience. Chess is like learning a whole new language.
In my opinion, the reason adults "typically" improve at a slower rate than kids is most likely because we tend to have other commitments (full time job, family, etc) that prevent us from applying the same level of focus as kids who don't have the same conflicts that get in the way of their development. .
I'd say we also generally tend to cling to our mistakes. A 5 year old will try out an idea, have it blow up in their face, and move on. The older you get the more apprehensive some people are to try something new and original, even if their old ideas aren't necessarily good.